This invention generally relates to the art of electrical connectors and, particularly, to an electrical connector or electronic device wherein terminal pins are electrically coupled through holes in a flat circuit or substrate, such as a flat flexible circuit, along with a unique structure of the terminals themselves.
Numerous electrical connectors have been designed for utilization with a flat circuit which may be mounted directly on the connector or connected in circuit with terminal pins on the connector. An example of a flat circuit is a flat flexible circuit which includes a flat flexible dielectric substrate having one or more holes therein for receiving one or more terminal pins. A ductile conductive film or other circuit trace system is deposited on the substrate in an area at least about the hole or holes. The terminal pins are inserted into the holes in the substrate to establish electrical and mechanical connections between the pins and the flat flexible circuit. Typically, each hole is smaller in diameter than a respective pin. Alternatively, the pin may be punched through the flat flexible circuit to establish the electrical and mechanical connection therewith.
In order to assure good electrical and mechanical connections in these types of electronic devices or electrical connectors, solder or other adhesives often are used. For instance, in U.S. Pat. No. 4,970,624, dated Nov. 13, 1990 and assigned to the assignee of the present invention, uni-axial adhesive is deposited on the flat flexible circuit about the hole which is penetrated by the terminal pin. The adhesive includes a non-conductive base incorporating randomly spaced conductive particles. When the terminal pin is forced through the adhesive, a portion of the adhesive is carried with the terminal pin between the pin and the flat flexible circuit. The carried portion of the adhesive is compressed for establishing contact between the conductive particles and, thereby, conductivity between the terminal pin and the flat flexible circuit, leaving the adhesive other than that portion in a non-conductive state. Such adhesives often are called xe2x80x9cZ-axisxe2x80x9d adhesives. These adhesive were developed to replace soldering techniques which require specific temperature resistant components and substrates.
Conductive adhesives are used in other applications involving flat flexible circuits. For instance, in U.S. Pat. No. 5,456,616, dated Oct. 10, 1995 and assigned to the assignee of the present invention, the connector housing is fabricated of a die cast metallic material, such as of magnesium, aluminum or the like. The ductile film on the flat flexible circuit is fabricated of a different metallic material, such as copper or the like and, in fact, may be plated with still a different metallic material such as a tin/lead alloy. The conductive film on the flat flexible circuit acts as a ground plane against the rear face of the connector housing. The housing has a plurality of pins which project through holes in the flat flexible circuit. Using a xe2x80x9cZ-axisxe2x80x9d adhesive between the housing pins and the flat flexible circuit not only is expensive, as described above, but the conductive interface between the different metal components is limited to the areas of pressure. Consequently, that patent teaches the use of an omni-directional conductive adhesive deposited on the conductive film over the areas of the holes therein, the conductive adhesive expanding the conductive interface between the metal housing and the metal ground plane defined by the conductive film.
Although such uses of conductive adhesives, whether the adhesives are Z-axis adhesives or omni-directional adhesives, serve their intended purposes in certain applications, they are relatively expensive both in the cost of the adhesives as well as their methods of use. In addition, the use of either type of conductive adhesive is costly in terms of secondary operations and costs associated with the metal particles, not to mention the problem of clogging adhesive dispensers by the metallic particles.
Because of the problems associated with the use of conductive adhesives, a unique system was devised as disclosed in U.S. Pat. No. 5,384,435, dated Jan. 24, 1995 and assigned to the assignee of the present invention. That patent solves the problems with conductive adhesives by establishing an electrical connection directly between the terminal pin and the flat conductor on the flat flexible substrate by controlling various parameters between the pin and the substrate. Although this system has proven quite effective, there remains a continuing problem in electrical connectors or electronic devices wherein the pins are very closely spaced, i.e., in very high density connectors. In particular, if the interference between a pin and the substrate produces a stress in the substrate, the stress is magnified in high density applications and results in what is called a systematic stress that causes stress concentrations and can even result in substrate fractures. The present invention is directed to solving this myriad of problems in an extremely simple manner by producing an electrical connection between a contact pin and a flat circuit exclusively by compression which results in no stress being imparted to the substrate of the flat circuit. This unique system can be used in a wide variety of applications as will be seen herein.
An object, therefore, of the invention is to provide a new and improved electrical connector for a flat circuit.
Another object of the invention is to provide a new and improved terminal for use with flat circuits.
In the exemplary embodiment of the invention, the connector and the terminal are used with a flat circuit having at least one pin-receiving hole therein and a conductor on a side thereof about the hole. The connector includes a dielectric circuit support member for supporting the flat circuit on one side thereof, with the conductor of the circuit facing away therefrom. The support member has a pin-receiving hole for registry with the pin-receiving hole in the flat circuit.
A conductive terminal is provided with a pin portion insertable from the one side of the support member through the hole in the flat circuit and into the hole in the support member. The terminal includes a laterally projecting wing portion for engaging the conductor on the flat circuit. The invention contemplates that the hole in the support member be sized relative to the cross-dimensions of the pin portion of the terminal to establish an interference fit therebetween and to maintain the wing portion of the terminal in compressive engagement with the conductor of the circuit. Therefore, the circuit is not in any way deformed which might cause stresses therein.
As disclosed herein, the circuit support member is fabricated of plastic material and the terminal is fabricated of metal material. The terminal may be stamped of conductive sheet metal material, including a pair of the wing portions projecting laterally from opposite sides thereof.
The terminal defines a longitudinal axis running lengthwise through the pin portion thereof. In one embodiment of the invention, the wing portion or portions are formed at an angle to the axis and at an angle to the flat circuit to provide a spring characteristic in the wing portions. In another embodiment, a resilient layer is sandwiched between the flat circuit and the one side of the support member.
According to one aspect of the invention, the terminal includes a contact pin extending coaxially from the pin portion of the terminal beyond an opposite side of the support member for interconnection to a contact of an appropriate complementary connecting device. The cross-dimensions of the contact pin are less than the size of the hole in the circuit support member so that the contact pin does not engage the inside of the hole when the pin portion of the terminal is inserted into the hole. This arrangement will prevent any plating on the contact pin from being scraped off of the pin when inserted into the hole.
According to another aspect of the invention, the terminal includes a head portion joined to the pin portion by a spring portion extending away from the one side of the circuit support member. The head portion is configured for engaging a conductor of a complementary electrical device. For instance, the head portion may have a flat surface generally parallel to the one side of the circuit support member for engaging a conductor of a second flat circuit.
Finally, with the terminal being stamped of sheet metal material, the terminal can be stamped with at least one laterally projecting shoulder portion spaced from the wing portion of the terminal. The shoulder portion can be used for engagement by an appropriate tool to facilitate inserting the pin portion of the terminal into the hole in the circuit support member.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.